1. Field of the Invention
The present invention relates to a semiconductor device having an interconnection and a via plug, and a manufacturing method thereof
2. Description of the Related Art
In recent years, to meet the requirements for higher speed of semiconductor elements, low-resistance materials such as copper have become widely utilized as the metal for interconnections. However, because etching copper is difficult, interconnection layers are normally formed through a so-called damascene process.
In a semiconductor device wherein copper interconnection layers are laid through the damascene process, every interconnection layer is required to have a via plug so as to connect to the other layers. The metal material normally employed for the via plug is copper or tungsten. Tungsten is particularly in wide use, as it has the advantage of good adaptability to fill up any space.
FIG. 2 shows a conventional copper interconnection structure with a tungsten plug. In the structure shown in the drawing, a silicon oxide film 1a, a silicon oxynitride (SiON) film 11, a silicon oxide film 1b, a silicon oxynitride film 12, a silicon oxide film 1c, a silicon oxynitride film 13 and a silicon oxide film 1d are laid in this order on a semiconductor substrate that is omitted from the drawing.
Within the silicon oxide film 1a, there is formed a contact plug connecting with a diffusion layer of the semiconductor substrate. The contact plug is composed of a barrier metal film 6a made of Ti/TiN and a tungsten film 3a. Within the silicon oxide film 1b, a first copper interconnection connecting with the upper surface of the above-mentioned contact plug is formed. The first copper interconnection is composed of a tantalum-based barrier metal film 4a and a copper film 5a. Within the silicon oxide film 1c, there is formed an interlayer via plug connecting the upper surface of the first copper interconnection. The interlayer via plug is composed of a titanium-based barrier metal film 6b and a tungsten film 3b. Within the silicon oxide film 1d, a second copper interconnection connecting with the upper surface of the interlayer through hole is formed. The second copper interconnection is composed of a tantalum-based barrier metal film 4b and a copper film 5b. 
Now, referring to FIGS. 10 to 12, a manufacturing method of the conventional interconnection structure of FIG. 2 is described below.
FIG. 10(a) is a cross-sectional view illustrating the step of the manufacturing method at a stage where formation of the contact plug and the first copper interconnection has completed. The steps which bring the state of FIG. 10(a) are first described. Firstly, after a silicon oxide film 1a is grown on a semiconductor substrate (not shown in the drawing) where elements such as a transistor are formed, a through hole is formed by dry etching, and then a barrier metal film 6a and a tungsten film 3a are formed in this order so as to fill up the inside of the through hole. Subsequent planarization is carried out by the CMP (Chemical Mechanical Polishing) and thereby formation of a tungsten plug is accomplished. Next, after growing a silicon oxynitride film 11 and a silicon oxide film 1b, an interconnection trench is formed within these films and, then, a tantalum-based barrier metal film 4a for which layers of Ta and TaN are laid in this order and a copper film 5a are formed in this order so as to fill up the inside of the trench. Subsequent planarization by the CMP accomplishes formation of a copper interconnection. Next, after a silicon oxynitride film 12 and a silicon oxide film 1c are grown, a resist film 15 patterned into a prescribed shape is formed thereon, and thus, the state of FIG. 10(a) is attained.
Subsequently, dry etching with a fluorocarbon-based gas is carried out till the silicon oxynitride film 12 is exposed and a through hole 16 is formed, and then, by means of oxygen plasma ashing or the like, the resist film 15 is removed.
Next, using a different etching gas, the silicon oxynitride film 12 is etched (FIG. 10(c)).
Subsequently, after a titanium film is grown over the entire surface of the silicon oxide film 1c by the sputtering method, a titanium nitride film is grown by the reactive sputtering method. The reactive sputtering method herein is carried out by using a Ti target and making the sputtered particles therefrom react with nitrogen before reaching the semiconductor substrate. In this manner, formation of a titanium-based barrier metal film 6b composed of layers of titanium/titanium nitride is accomplished.
Next, a tungsten film 3b is deposited (FIG. 11(a)). As the material gads thereat, a gas containing WF6 is, for example, utilized. The deposition of the tungsten film is normally carried out in two steps, the step of forming growth nuclei and the step of forming a bulk tungsten film.
First, the step of forming growth nuclei is performed. In this instance, the growth gas utilized is a mixed gas of WF6, SiH4 and Ar, and the deposition temperature (substrate temperature) is set at about 450xc2x0 C. When a tungsten film is grown to a prescribed thickness under these conditions, the supply of the gas is, at any rate, once stopped, and thereby the step of forming growth nuclei terminates.
Following that, with WF6 and H2 being supplied to the deposition chamber, a bulk tungsten film is grown to fill up the inside of the hole. This reaction is normally made under the H2 reducing condition where the growth rate of the film is faster than that in the step of growing nuclei. In this instance, the growth gas utilized is a mixed gas of WF6, H2 and Ar, and the deposition temperature (substrate temperature) is set at about 450xc2x0 C. Now, with this film growth, the inside of the through hole is completely filled up with tungsten. Next, by polishing the tungsten film by the CMP, the portion of the tungsten film 3b lying outside of the through hole is removed so that the tungsten film 3b is left only in the through hole, which accomplishes formation of a tungsten plug (FIG. 11(b)).
Next, after growing a silicon oxynitride film 13 and a silicon oxide film 1d, an interconnection trench is formed within these films (FIG. 12(a)) and, then, a tantalum-based barrier metal film 4b for which layers of Ta and TaN are laid in this order and a copper film 5b are formed in this order so as to fill up the inside of the trench (FIG. 12(b)). Subsequent planarization by the CMP accomplishes formation of an upper layer copper interconnection (FIG. 12(c)). Formation of a semiconductor device having interconnections and a tungsten plug is thereby accomplished.
The conventional technique described above has, however, problems that, in the region between the tungsten film 3b and the copper film 5a of FIG. 2, the titanium-based barrier metal film 6b may become degenerate and besides, the section of the copper film 5a that is in contact with the titanium-based barrier metal film 6b may become corroded. The occurrence of degeneration of the barrier metal film as well as corrosion of the copper film of these sorts has not been fully recognized thus far, but the investigation conducted by the present inventors confirmed that such phenomena indeed take place. It is considered that these phenomena result from the fact that a titanium-based material and copper are liable to react with each other. When the standard steps of growing films in the prior art are employed, the titanium-based material and copper interact rapidly and excessively, which leads to the degeneration of the barrier metal film and the corrosion of the copper film. Consequently, the conventional technique described above has the following problems.
The first problem is a lowering of electromigration resistance in the region between the tungsten film 3b and the copper film 5a, since the electromigration resistance becomes low in the degenerated section of the barrier metal film as well as in the corroded section of the copper film.
The second problem is the proneness of the detachment of films on the interface between the titanium-based barrier metal film 6b and the copper film 5a. This is caused by poor adhesion the degenerated section of the barrier metal film has to the tungsten film and the like, together with poor adhesion the corroded section of the copper film has to the barrier metal film. Because of this, when subjected to heating in the later steps of growing films and the like, or during the step of wire bonding after completion of the chip fabrication, stress may be applied to the region between the via plug and the copper interconnection, which makes the detachment liable to happen.
The third problem is an increase in contact resistance on the interface between the titanium-based barrier metal film 6b and the copper film 5a as well as an increase in interconnection resistance of the copper interconnection. This is brought about by high electrical resistance of the degenerated section of the barrier metal film and that of the corroded section of the copper film.
In short, the conventional technique is accompanied with the problems that, on the interface between the copper interconnection and the via plug, the electromigration resistance may be lowered, the detachment may become liable to happen, and the contact resistance and the interconnection resistance may be increased.
The above problems may become even greater due to a factor in the step described below. After etching for the removal of the silicon oxynitride film 12 is completed as seen in FIG. 10(c), the step of removing the etching residue is normally performed, using a resist stripper agent such as an amine-containing agent. Such a treatment, however, oxidizes or degenerates the exposed surface of the copper film and reduces the adhesion between the barrier metal film and the copper film further. That is, to the reduction of adhesion resulting from the interaction between the material of the barrier metal film and copper, a further reduction of adhesion caused by the peeling agent is added. Therefore, if the above step is employed, problems of the lowering of electromigration resistance, the occurrence of the detachment and increases in contact resistance and interconnection resistance become greater.
Meanwhile, along with the element miniaturization, thinning of the copper film is presently proceeding so that even a slight increase in contact resistance between the barrier metal film and the copper film or in interconnection resistance considerably hinders the high-speed operation of the elements. Therefore, the problem of the increase in resistance that is brought about by the reduction of adhesion between the barrier metal film and the copper film becomes particularly significant when the copper film is made thin, for example, when its film thickness is not exceeding 300 nm.
Accordingly, an object of the present invention is to increase adhesion on the interface between a copper interconnection and a via plug that is formed thereon, and thereby achieve an improvement of the electromigration resistance, an improvement of adhesion and reductions of contact resistance as well as interconnection resistance.
In light of the above problems, the present invention provides a semiconductor device which has, on a semiconductor substrate:
an interconnection layer made of copper-based metal; and
a via plug formed in contact with the upper surface of said interconnection layer; wherein,
said via plug comprises a conductive film and a barrier metal film that covers the lateral and bottom surfaces of said conductive film; and
said barrier metal film covering the bottom surface of the conductive film and said interconnection layer are separated by an alloy layer made through the reaction of the material of said barrier metal film and said copper-based metal.
In the semiconductor device of the present invention, the introduction of an alloy layer made through the reaction between the material of the barrier metal film and copper-based metal markedly improves adhesion between the interconnection layer and the via plug, and attains an improvement of the electromigration resistance, an improvement of adhesion and reductions of contact resistance as well as interconnection resistance.
Hitherto, it has been hardly recognized that the titanium-based material constituting the barrier metal film reacts with copper and an alloy layer is formed. In consequence, a feasibility of a technique to improve adhesion between the via plug and the interconnection layer through an appropriate control over the reaction of alloy layer formation or practical methods to perform such an appropriate control over the reaction of alloy layer formation has little studied. The present inventors made various investigations over these matters and, as a result, found out that, if an alloy layer is formed with its film thickness well under control, adhesion between the interconnection layer and the via plug can be improved with effect and reached the present invention.
The investigations by the present inventors indicate that the alloy layer made through the reaction of the material of the barrier metal film and copper is formed with the barrier metal film material and copper interacting each other in the vicinity of the surfaces of the barrier metal film and the copper interconnection. It should be noted, however, that a mere formation of an alloy layer alone cannot improve adhesion between the interconnection layer and the via plug sufficiently, and production of a layered structure in which an alloy layer and a barrier metal film are laid over the copper interconnection in this order is called for. In other words, it is essential to leave a part of the barrier metal film that lies under the conductive film and constitutes the via plug as an unreacted layer. Referring to FIG. 13, this point is further described below.
In FIG. 13, within a silicon oxide film 41, there is formed a copper interconnection layer in which a copper film 43 is embedded over a barrier metal film 42 in the form of damascene. A silicon oxide film 44 is applied over that and an interlayer via plug connecting with the upper surface of the copper interconnection is formed therein. The interlayer via plug comprises a barrier metal film 46 and a tungsten film 47. If the material of the barrier metal film and copper interact excessively, the resulting structure becomes the one shown in FIG. 13(b), wherein the tungsten film 47 and an alloy layer 45 come to direct contact with each other. Since adhesion between the tungsten film 47 and the alloy layer 45 is not good, with such a structure, it is difficult to solve the problems of the electromigration resistance, the interface detachment and the increases of contact resistance and interconnection resistance. Therefore, in a semiconductor device of the present invention, the interconnection layer and the barrier metal film covering the bottom surface of the conductive film are separated by an alloy layer made through the reaction of the material of the barrier metal film and copper, making up a layered structure in which copper-based metal, the alloy layer and the barrier metal film are laid in this order. That is, as shown in FIG. 13(a), there is formed a structure in which the barrier metal film 46 is interposed between the tungsten film 47 and the alloy layer 45. It is due to such a structure that adhesion between the interconnection layer made of copper-based metal and the via plug formed thereon can be improved, and, consequently, an improvement of the electromigration resistance, an improvement of adhesion and reductions of contact resistance as well as interconnection resistance can be achieved.
As described above, in the present invention, an alloy layer that contributes to an improvement of adhesion is formed, whole a part of the barrier metal film is left as an unreacted layer, and, thus, a layered structure of an alloy layer and an unreacted layer of the barrier metal film is provided. The structure of this sort can be obtained by choosing an appropriate deposition temperature for the conductive film that constitutes the via plug, with the film thickness and the deposition method of the barrier metal film taken into consideration.
Further, the present invention provides methods of manufacturing a semiconductor device with an afore-mentioned structure, as follows.
Namely, the present invention provides a method of manufacturing a semiconductor device, which comprises the steps of:
forming an interconnection layer of copper-based metal on a semiconductor substrate;
forming an insulating film over said interconnection layer and thereafter, within said insulating film, making a through hole down to said interconnection layer;
growing a titanium-containing barrier metal film over the entire surface and thereafter growing a conductive film over said barrier metal film so as to fill up said through hole; and
performing either chemical mechanical polishing or etching back in such a way that said conductive film is left only inside of said through hole; wherein,
in the step of growing said conductive film, concurrently with growing the conductive film, a part of the barrier metal film is made to react with said copper-based metal so that, at the bottom of said through hole, there is formed a layered structure in which an alloy layer made through the reaction of copper-based metal and titanium and an unreacted layer of the barrier metal film are laid in this order.
The titanium-based material is highly reactive to copper. Therefore, in the case that tungsten is employed as the material of the via plug in the conventional method, in the step of growing a tungsten film, the titanium-based material constituting the barrier metal film reacts with copper excessively, and the titanium-based material under the tungsten plug is completely used up for the reaction. Furthermore, because the titanium-based material and copper interact very rapidly, it is difficult to obtain a reactive layer of high film quality, possible to contribute to an improvement of the interface adhesion. In contrast with this, the present invention can sufficiently improve the adhesion between the interconnection layer and the via plug, since, at the bottom of the via plug, there is formed a structure in which an alloy layer made through the reaction of the copper-based metal and titanium and a barrier metal film are laid in this order.
Further, the present invention provides a method of manufacturing a semiconductor device, which comprises the steps of:
forming an interconnection layer of copper-based metal on a semiconductor substrate;
forming an insulating film over said interconnection layer and thereafter, within said insulating film, making a through hole down to said interconnection layer;
growing a tantalum-containing barrier metal film over the entire surface and thereafter growing a conductive film over said barrier metal film so as to fill up said through hole; and
performing either chemical mechanical polishing or etching back in such a way that said conductive film is left only inside of said through hole; wherein,
in the step of growing said conductive film, concurrently with growing the conductive film, a part of the barrier metal film is made to react with said copper-based metal so that, at the bottom of said through hole, there is formed a layered structure in which an alloy layer made through the reaction of copper-based metal and tantalum and an unreacted layer of the barrier metal film are laid in this order.
In this invention, a tantalum-based material is utilized for the barrier metal film. As the material for the barrier metal film in the tungsten plug, titanium-based materials have been, hitherto, widely used. However, reactivity of titanium to copper is considerably high so that there are instances where it is difficult to control the reaction of the alloy layer formation with a high accuracy. For example, in depositing titanium into the through hole, the titanium-based film at the bottom of the hole may not grow sufficiently thick and the film thickness thereof may remain thin. In such a case, the titanium-based film is liable to be used up for the reaction of the alloy layer formation, and the layered structure in which the alloy layer and the barrier metal film are laid in this order becomes difficult to obtain. Against this, if a tantalum-based material is employed as the material for the barrier metal film, the reaction of the alloy layer formation proceeds gently so that the reaction can be controlled with a high accuracy and the layered structure in which the alloy layer and the barrier metal film are laid in this order can be obtained with relative ease. Further, because the alloy layer made through the reaction of tantalum and copper surpasses the alloy layer made through the reaction of titanium and copper in mechanical strength and adhesion with other films, the effects of an improvement of the electromigration resistance, an improvement of detachment resistance and the reductions of contact resistance as well as interconnection resistance, for this particular invention, become more pronounced.
In either of the above methods of manufacturing a semiconductor device according to the present invention, in the step of growing a conductive film, concurrently with growing a tungsten film, a part of the barrier metal film is made to react with the copper-based metal so that, at the bottom of the through hole, there is formed a layered structure in which an alloy layer made through the reaction of copper-based metal and the material of the barrier metal film and the barrier metal film are laid in this order. The layered structure of this sort can be obtained through an appropriate control over the reaction of the alloy layer formation.
The control of the reaction of the alloy layer formation can be made by choosing the film thickness and the deposition method of the barrier metal film, the deposition conditions of the conductive film (tungsten or the like) that fills up the via plug and the like in an appropriate manner. Nevertheless, it is particularly important that the optimum deposition temperature for the conductive film is chosen, with the film thickness and the deposition method of the barrier metal film taken well into consideration, because the reaction of the alloy layer formation proceeds mostly at the time of growing the conductive film. Although the reaction of the alloy layer formation can be controlled through conditions for a heat treatment performed in one of the steps after completing the formation of the conducive film, this can hardly provide a good control of the film thickness of the alloy layer with a high accuracy. Meanwhile, the investigations of the present inventors revealed that the crucial factor to control the film thickness of the alloy layer with a high accuracy is the deposition temperature and the like at the time a conductive film of tungsten or the like is grown over the barrier metal film after completion of its growth, and further confirmed that, by controlling that, an alloy layer can be formed with its film thickness well under control.
The deposition temperature of a conductive film as used herein is the deposition temperature xe2x80x9cin the step of growing a conductive film so as to fill up the through holexe2x80x9d, and, for example, when tungsten is utilized as the material of the conductive film, it is the deposition temperature of a bulk tungsten film. The deposition of the tungsten film inside of the through hole is normally carried out in two steps, the step of forming a tungsten film for the formation of growth nuclei and the step of forming a bulk tungsten film to fill up the hole. In short, in order to control the reaction for the alloy layer formation and control its film thickness well, the deposition temperature in the step of forming a bulk tungsten film is important.
Further, a copper-based metal film as used in the present invention is a film whose main component is copper and whose copper content is not less than 90% by weight. Further, in the present invention, as a conductive film, a tungsten film, for example, can be employed.